Surface Enhanced Raman Spectroscopy (SERS), surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR) measurement techniques are very sensitive techniques to measure small molecules, even at the single molecule level. SERS is a surface sensitive technique which results in the enhancement of Raman scattering by materials adsorbed or bound, i.e., in close contact with or in the vicinity of metal surfaces. In surface enhanced Raman scattering the local electromagnetic field is greatly enhanced at a metal surface. In Surface Plasmon Resonance, light interacts with a metal surface, giving rise to collective oscillations of electrons at the surface. The angle of reflection depends on the dielectric constant of the materials adsorbed on the surface of the metal film. LSPR is a phenomenon whereby light interacts with a nanostructure, giving rise to coherent localized plasmon oscillations with a resonant frequency that strongly depends on the composition, size, geometry, dielectric environment and separation distance of the nanostructure. SPR and LSPR have been used for chemical and biological sensing of molecules, proteins, DNA/RNA, viruses, microorganisms and cells. Both techniques are extremely useful for following binding kinetics and for real-time molecule detection.
The state of the art comprises two types of plasmonic or surface enhanced Raman sensing devices. A first type uses a sensing surface that is covered with a thin metal film such as gold or silver. The thin metal film is used for sensing purposes. A second type uses patterned metal structures or patterned structures that are coated with metal nanoparticles. These nanoparticles are used for sensing purposes. For example, Schmidt et al. (“Towards easily reproducible nano-structured SERS substrate”, 2009 IEEE Sensors, Pages: 1763-7) describes a SERS substrate wherein pillars are coated with a thin metal film for enhancing the Raman effect.
To propagate a fluid sample through these devices, other MEMS components such as flow cells, fluidic channels or pumps are necessary. These components increase the size and cost of the device. As the total cost of these devices is high, they cannot be used as disposable devices.